Sealing gland with unstressed standby seal

ABSTRACT

A sealing gland assembly for an aircraft undercarriage leg in which, in addition to the primary or working seal ring, a standby seal ring is stored in an unstressed condition on the &#39;&#39;wet&#39;&#39; side of the working seal ring. Both seal rings are contained within a seal chamber formed by an enlargement at the end of the outer tube of a sliding telescopic pair of tubes, the open end of the enlargement being substantially closed by a gland ring that has an axial flange extending into the seal chamber and compressing the working seal, but not the standby seal, against the inner tube.

United States Patent 1 1 Mar. 27, 1973 Cameron-Johnson [54] SEALINGGLAND WITH UNSTRESSED STANDBY SEAL [75] Inventor: Alan Cameron-Johnson,St. Albans,

England [73] Assignee: Hawker Siddeley Aviation LimiteKingston-upon-Thames, Surrey, England [22] Filed: Mar. 3, 1971 [21]App1.No.: 120,460

[30] Foreign Application Priority Data Mar. 6, 1970 Great Britain..10,888/70 s2 us. Cl. ..27'//9, 277/11 [51] Int. Cl. ..Fl6j 9/00 [58]Field of Search ..277/l 9, ll

[56] References Cited UNITED STATES PATENTS 3,514,114 5/1970 Monahan..277/9 X Primary Examiner-Meyer Perlin Assistant Examiner-Ronald C.Capossela Attorney-Rose & Edell [57] ABSTRACT A sealing gland assemblyfor an aircraft undercarriage leg in which, in addition to the primaryor working seal ring, a standby seal ring is stored in an unstressedcondition on the wet side of the working seal ring. Both seal rings arecontained within a seal chamber formed by an enlargement at the end ofthe outer tube of a sliding telescopic pair of tubes, the open end ofthe enlargement being substantially closed by a gland ring that has anaxial flange extending into the seal chamber and compressing the workingseal, but not the standby seal, against the inner tube.

8 Claims, 1 Drawing Figure Patented March 27, 1973 nmenmuuuu 'V/lInventor ALAN CAMER 0N 0 0 H N50 6? M Allorney:

SEALING GLAND WITH =UNSTRESSED STANDBY SEAL 4 This invention relates toaircraft undercarriage legs and like hydraulic units. More particularly,it is concerned with the provision of standby sealing glands for suchunits.

The current emphasis on reliability and minimum down time of aircrafthydraulic and undercarriage equipment has necessitated the provision ofin situ replacement or standby seals which can be put into operationwith minimum dismantling and during a quick turnaround.

One known arrangement employs two seals within the unit in a primary andsecondary capacity. The seals lie in positions adjacent to one anotherand both are in stalled in their actual working condition. Ideally, thesecondary seal automatically performs its sealing function as soon asthere is primary seal failure. This technique has several importantdisadvantages, as follows:

a. Both seals are constantly under stress in that they have beencompressed within or stretched over a supporting ring. v

b. The location of the secondary seal relative'to the primary seal issuch that primary failure need not be evident as the secondary seal willtend to disguise a primary leakage, being normally located on the dryside of the unit.

c. If the primary seal is functioning correctly the secondary seal canbe working in undesirably dry conditions, which may result in itbecoming worn out before commencing'operation.

According to the present invention, a replacement or standby seal islocated within the unit on the wet side of the primary seal. Thisdiffers from the arrangement previously described in that the standbyseal, although adjacent to the working seal, is only stored within theunit and is, indeed, stored in good conditions within the wet region.

Preferably, the standby seal is unstressed. By this we mean that it isneither compressed within nor stretched over a supporting ring. Thispermits the use of polytetrafluorethylene and other low stretchmaterials without introducing difficulties arising from slow recoverycharacteristics.

Because of its location relative to the primary seal, i.e., on the wetside side the unit, the standby seal does not disguise any leakage orfailure of the primary seal, nor will it be worn out before functioningas can be the case with the previous arrangement. The fact that thestandby seal may be in rubbing contact with a sliding tube of the unitis not in itself detrimental as the seal material is unstressed and canbe subjected in this way to a desirable running in process before beingrequired to function. This is particularly advantageous withpolytetrafluorethylene or other relatively hard sealing surfaces.

The ability to store replacement seals within a hydraulic unit is ofgreat benefit when that -unit could be working in areas lacking incomprehensive stores. In the case of an aircraft operating from a remoteairfield, for example, a fairly rapid replacement can be made withoutthe aircraft becoming unserviceable and this could apply to any piece ofhydraulic equipment employing similar methods.

One arrangement in accordance with the invention will now be describedby way of example. Reference will be made to the accompanying drawingwhich represents the lower portion of an aircraft oleo undercarriage legand is a side elevation sectioned to disclose the seal glandinstallation.

A wheel axle 1 is united as part of an overall machined member to asliding tube 2. This tube forms the inner sleeve of the undercarriageleg and moves along its longitudinal axis within the undercarriage legcylinder 3. The leg cylinder 3 is enlarged in diameter at its lower endregion to form a seal chamber 4 and has, at its extreme lower end, anattachment flange ring 5. Secured to this flange 5 by a ring of bolts isthe seal gland assembly, comprising a machined ring 6 having an axialflange formed with an external recess to accommodate a seal ring 10 andhousing the main seal assembly 9. Additionally, there is a lowermachined ring 7, recessed adjacent to the sliding tube 2 to retain ascraper ring 8 when the gland is assembled.

in the assembled condition the main (or primary) seal assembly 9 iscompressed between the axial flange of the ring 6 and the sliding tube2. The seal ring 10 prevents the seepage of fluid through the boltedjoint.

The standby seal assembly 11 isdisposed within the seal chamber 4 on thewet side of the main seal 9. it is shown uncompressed, with a nominalclearance 12 between itself and the sliding tube 2, and it is separatedfrom the mainseal assembly 9 by a split ring 14 that is, in turn,located by a spacer ring 13 encircling the standby seal assembly. Thespacer 13 is channelled to provide a leakage path allowing the passageof fluid to the main seal assembly past the standby seal.

In order to replace'seals the aircraft is jacked up and the oleo legdeflated. The ring of bolts connecting the seal gland assembly to theundercarriage leg is removed and the whole seal gland assembly iswithdrawn and moved down along the sliding tube to disclose both seals.The defective main seal 9 is cut away, the split ring 14 removed and thestandby seal 11 assembled in place of the defective element. The splitring 14 is then repositioned leaving the standby seal space empty. The

whole assembly is then refitted to the leg cylinder 3.

During this operation fluid loss from the leg will be small because ofthe provision of a close fitting bush 15 between the leg cylinder 3 andsliding tube 2 just above the seal assembly. This bush may besupplemented by a piston ring type of oil barrier, if desired.

The insertion of another standby'seal into the storage space can beperformed at the next convenient service time. The method isparticularly applicable to an aircraft hydraulic installation but it canequally be applied to any commercial hydraulic equipment functioning ina like manner.

1. A sealing gland of an hydraulic unit, comprising an outer tube havinga normal diameter portion, an inner member sliding telescopically withinsaid outer tube, an annular seal chamber formed around the inner memberby an enlarged diameter portion at one end of the outer tube a shoulderbeing defined between said normal and enlarged diameter portions, aprimary working seal housed in said seal chamber to prevent egress ofhydraulic fluid through said end of the outer tube from the annularspace between said inner member and outer tube, a replacement seallikewise housed in said seal chamber, the primary and replacement sealsbeing disposed alongside one another with the primary seal locatednearer said end of the outer tube so that the replacement seal is wettedby the hydraulic fluid, and means compressing only the primary sealradially into sealing engagement with said inner member, the replacementseal being in substantial rubbing contact with said inner member andbeing substantially un stressed.

2. A sealing gland according to claim 1, wherein on the side of thereplacement seal opposite to the primary seal a close fitting bush isprovided between the inner member and the normal diameter portion of theouter tube to minimize leakage when the gland is opened for removal ofthe primary seal and fitting of the replacement seal in its place.

3. A sealing gland according to claim 1, wherein the replacement seal issituated between the primary seal and a radial end wall of the sealchamber provided by the shoulder where the normal and enlarged diameterportions of the outer tube meet, and the two seals are separated fromone another by an annular member, such as a split ring, removably fittedwithin the seal chamber.

4. A sealing gland according to claim 3, wherein said annular member isspaced from said end wall of the seal chamber by a spacer ringencircling the replacement seal, which spacer ring is channelled toallow the axial passage of fluid to the primary seal.

5. A sealing gland according to claim 1, wherein said compressing meanscomprises a gland ring secured to said end of the outer tube and havinga flange extend ing axially into the seal chamber between the primaryseal and said enlarged diameter portion of the outer tube.

6. A sealing gland according to claim 5, wherein an auxiliary seal ringis provided between the flange on the gland ring and the surroundingwall of the seal chamber.

7. A sealing gland according to claim 5, wherein a scraper ring engagesthe inner member on the side of the primary seal opposite to the'replacement seal, which scraper ring is carried by the gland ring.

8. A sealing gland of an hydraulic unit, comprising inner and outertelescopically sliding members, the outer member being in the form of atube, enclosure means provided at one end of a first one of said innerand outer telescopically sliding members and defining together with thesecond one of said telescopically sliding members on annular sealchamber, a primary working seal housed in said seal chamber, areplacement seal likewise housed in said seal chamber alongside saidprimary seal, the primary seal being located between said replacementseal and said one end of said first one of said telescopically slidingmembers, and means stressing only said primary seal thereby pressing itradially i'nto sealing engagement with the second one of saidtelescopically sliding members, the replacement seal being substantiallyunstressed.

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1. A sealing gland of an hydraulic unit, comprising an outer tube havinga normal diameter portion, an inner member sliding telescopically withinsaid outer tube, an annular seal chamber formed around the inner memberby an enlarged diameter portion at one end of the outer tube a shoulderbeing defined between said normal and enlarged diameter portions, aprimary working seal housed in said seal chamber to prevent egress ofhydraulic fluid through said end of the outer tube from the annularspace between said inner member and outer tube, a replacement seallikewise housed in said seal chamber, the primary and replacement sealsbeing disposed alongside one another with the primary seal locatednearer said end of the outer tube so that the replacement seal is wettedby the hYdraulic fluid, and means compressing only the primary sealradially into sealing engagement with said inner member, the replacementseal being in substantial rubbing contact with said inner member andbeing substantially unstressed.
 2. A sealing gland according to claim 1,wherein on the side of the replacement seal opposite to the primary seala close fitting bush is provided between the inner member and the normaldiameter portion of the outer tube to minimize leakage when the gland isopened for removal of the primary seal and fitting of the replacementseal in its place.
 3. A sealing gland according to claim 1, wherein thereplacement seal is situated between the primary seal and a radial endwall of the seal chamber provided by the shoulder where the normal andenlarged diameter portions of the outer tube meet, and the two seals areseparated from one another by an annular member, such as a split ring,removably fitted within the seal chamber.
 4. A sealing gland accordingto claim 3, wherein said annular member is spaced from said end wall ofthe seal chamber by a spacer ring encircling the replacement seal, whichspacer ring is channelled to allow the axial passage of fluid to theprimary seal.
 5. A sealing gland according to claim 1, wherein saidcompressing means comprises a gland ring secured to said end of theouter tube and having a flange extending axially into the seal chamberbetween the primary seal and said enlarged diameter portion of the outertube.
 6. A sealing gland according to claim 5, wherein an auxiliary sealring is provided between the flange on the gland ring and thesurrounding wall of the seal chamber.
 7. A sealing gland according toclaim 5, wherein a scraper ring engages the inner member on the side ofthe primary seal opposite to the replacement seal, which scraper ring iscarried by the gland ring.
 8. A sealing gland of an hydraulic unit,comprising inner and outer telescopically sliding members, the outermember being in the form of a tube, enclosure means provided at one endof a first one of said inner and outer telescopically sliding membersand defining together with the second one of said telescopically slidingmembers on annular seal chamber, a primary working seal housed in saidseal chamber, a replacement seal likewise housed in said seal chamberalongside said primary seal, the primary seal being located between saidreplacement seal and said one end of said first one of saidtelescopically sliding members, and means stressing only said primaryseal thereby pressing it radially into sealing engagement with thesecond one of said telescopically sliding members, the replacement sealbeing substantially unstressed.